Fluidized bed



United States Patent Hans Geipel Oberhausen-Sterkrade;

Eckehard Forster, Oberhausen; Wilfried Heinemann, Duisburg-Hamborn; Kurt1 Baranowski, Essen-Frintrop, Germany [72] Inventors [21] Appl. No.821,700

[22] Filed May 5,1969

[45] Patented Dec. 29, 1970 [73] Assignee Huttenwerk Oberhausen A.G.

Oberhausen, Germany a corporation of Germany [32] Priority May 10, 1968[3 3 1 Germany Continuation-impart of Ser. No. 729,833, Jan. 25, 1968,now Patent No. 3,492,740

[54] FLUIDIZED BED 5 Claims, 1 Drawing Fig.

152 u.s.c1 2 3/21;

511 1m.c1 F27b3/00, F27b15/00 1501 FieldofSearchQ 1. 263/4OA. 2lA.2lC;165/104; 34/57A.57T

l 56] References Cited] UNITED STATES PATENTS 1,765,026 6/ l 930 Miller263/21C 2,600,306 6/1952 Lipscomb 263/8X Primary Examiner-John J. CambyAttorney-Karl F. Ross ABSTRACT: In a plant for the heat treatment ofworkpieces on a continuously moving apertured conveyor, the latter issurrounded by a fluidized bed of solid ceramic particles entrained by astream of carrier gas within a tunnel whose discharge end contains anoscillatable supporting plate, upwardly inclined toward the outlet,underneath the conveyor to stop the outward movement of solid particlesand accumulate them in a nearly stationary pile traversed by theemerging workpieces; escape of particles underneath the second conveyoris prevented by a flexible seal between the tunnel bottom and theoscillating plate.

PATENTE [1 02 9 I970 INVENTORS GEIPEL- HANS ECKEHARD FORSTER WILFRIEDHEINEMANN KURT BARANOWSKI ATTORNEY FLUIDIZED BED This application isacontinuation in part of copending application Ser. No. 729,833 filed 25Jan. 1968, now 11.8. Pat. No. 3,492,740.

ln commonly owned U.S. Pat. No. 3,492,740 there is disclosed a fluidizedbed for the heat treatment of workpieces, particularly but notexclusively the cooling of steel wire which is to be patented (i.e.cooled at a controlled rate) for transformation from its austeniticstate to a sorbitic pearlite structure as more fully disclosed incommonly owned application Ser. No. 675,522 filed 16 Oct; 1967, now US.Pat. No. 3,525,507.

The term fluidized bed" denotes a mass of solid particles, such asceramic granules, entrained by a'stream of carrier gas. The particles,which should have an elevated heat transfer coefficient, serve as theprincipal constituent of the cooling medium whereas the carrier gasplaysonly a minor role in the maintenance of the desired dischargetemperature. This gas is also used as a vehicle for a continuousrecirculation of the particles, generally in the direction of conveyormotion, through a cooling tunnel and through an external cooling chamberwhere the heat abstracted from the workpieces (e. g. a succession ofwire loops) is removed. For most effective heat transfer it is desirableto let these particles accumulate in a nearly stationary pile at theexit end of the tunnel and, preferably, also at the entrance end. At thesame time, for

reasons of economy as well as accurate control of the exit temperature,any escape of particles together with the emerging workpieces should besuppressed or at least minimized; thus, in the wirepatenting process ofour aforementioned copending application it is essential to completethe. transformation under substantially isothermic conditions, in theabsence of a cooling medium other than the surrounding atmosphere, sothat all contactwith accompanying solid particles should be positivelyterminated as soon as the workpieces leave the bed.

The general object of the present invention is to provide a fluidizedbed satisfying this requirement for the aforestated purpose and forother types of heat treatment, a term intended to encompass exposure toany contacting medium maintained at a predetermined temperature.

The solution of this problem proposed in US. Pat. No. 3,492,740 residesin the provision of two conveyors within the tunnel, i .e. a principalconveyor which is apertured to facilitate the circulation of heating orcooling medium around the workpieces carried thereon and which extendswithin the tunnel past the exit end thereof for discharging theheattreated workpieces, and a secondary conveyor located just below theprincipal conveyor at the exit end, this secondary conveyor moving in adirection opposite that of the principal conveyor so as to arrestoutwardly traveling particles which thereby pile up ahead of the tunnelexit.

Although this solution is satisfactory for most purposes, difficultiesmay arise from the necessity of sealing the region below the returningrun of the secondary conveyor against outgoing particles to preventtheir escape from the tunnel.

An object of our present improvement, therefore, is to provide analternate system which, in addition to satisfying the aforestateddesiderata, minimizes this problem of leakage.

in accordance with the present improvement, we replace the continuouslyrotating secondary conveyor by a vibratile support which is upwardlyinclined toward thetunnel exit underneath the apertured band referred tohereinabove as the principal conveyor," this support being oscillatableat a sufficiently high frequency to drive any outwardly travelingparticles back into the tunnel. With particle sizes on the order of 40to 160 microns, a suitable vibration frequency may range betweenapproximately and 40 c.p.s.

Since the oscillatory support, apart from its vibrations, remains at afixed location with reference to the tunnel wall,

the space underneath that support may be readily sealed with the aid ofa flexible strip spanning the intervening gap. Having no majorlongitudinal motion of its own, this support is found to define asharper and more constant profile for the pile of particles accumulatingthereon so that the duration of the heat treatment is more nearlyindependent of the extent to which the treated wire or other workpieceprojects above the supporting surface. We have found, therefore, thatwith the present improvement the quality of the product can besignificantly enhanced.

The invention will be described in greater detail with reference to theaccompanying drawing, the sole FIG. of

which is a diagrammatic side-elevational sectional view of a fluidizedbed for the cooling of wire in accordance with a preferred embodiment.-

The bed 1 shown in the drawing consists, essentially, of a mass of solidparticles (e.g. of magnesia 2) entrained by a stream of gas which flowstoward the discharge end 10 of a tunnel 15 traversed by an aperturedprincipal conveyor 5 in the form of an endless belt such as a wirescreen or a set of parallel wires. workpieces 6, i.e. a succession ofinterconnected loops of steel wire. are deposited on conveyor 5 near thetunnel entrance by a dispenser generally indicated as 16. This dispensercomprises a rotating; tubular arm through which the hot steel wirepasses so as to beformed into loops by the arm's rotation; moreelaborate types of loop formers are known, for example, from US. Pat.Nos. 3,056,433 and Re. 26,052. The dispenser 16 may oscillatetransversely with reference to conveyor 5, in the manner disclosed incommonly owned application Ser. No. 675,405 filed 16 Oct. 1967, for thepurpose of spreading the loops most effectively over the availableconveyor surface. t

A stream of relatively inert carrier gas, e.g. hydrogen or carbonmonoxide, is continuously recirculated through the tunnel 15 by way ofanentrance pipe 17 near the dispenser 16 and an exhaust pipe 18 at theexit end 10. A stationary imperforate support plate 7 underlies theupper run of belt 5 just below the inlet 17 so that solid particlesentrained by the carrier gas tend to accumulate as shown at 11.Additional gas is admitted via a manifold 3 at a controlled rate througha perforated base 4 on which the particles 2 come to rest. The particlesexhausted through outlet 18 and through a further exit port 20 arereturned to the inlet 17 after passing through a cooling chamber notshown; reference is made to the aforementioned copending applicationSer. No. 675,522 for additional details of a plant of which theillustrated arrangement forms a part.

Conveyor 5 rotates continuously so that its upper run carries theworkpieces 6, accompanied by some of the solid particles 2 of thefluidized bed 1, from the entrance end to the exit end of tunnel 15, Le.from left to right: as viewed in the drawing. A supporting plate 8 isinclinedly disposed at this exit end and carried by coil springs 21 onthe bottom 22 of tunnel 15. A vibrator, illustrated diagrammatically asarotating cam 23 acting upon a boss 24 of support 8, oscillates thelatter at 'a preferred rate of several tens of c.p.s. as indicated by anarrow A. A rubber strip 13 forms a flexible but tight seal between thetunnel bottom 22 and the underside of plate 8. The interior of thisplate may be compartmented, as shown, to form voids 25 to which furthercarrier gas may be admitted via flexible tubing, not shown, fordischarge into the space above plate 8 by way of orifices26.

The vibrations of plate 8 serve to arrest the outfiowing particlesentrained by conveyor band 5 which thereby accumulate in pile 12. Onemerging from this pile, the workpieces 6 undergo no further forcedcooling up to their discharge from the conveyor. The terminal portion oftunnel 15, beyond pile 12, thus may serve for the completion of theaustenitic pearlite transformation, under substantially isothermicconditions with inhibition of outward heat radiation by the thermallyreflecting tunnel walls, to prevent the formation of bainite, as morefully described in application Ser. No. 675,522 referred to above. Asalso described there, the temperature of the particles 2 and the speedof conveyor 5 may be regulated to maintain the desired exit temperaturefor'the workpieces, e.g. by means of a temperature sensor 19 disposednear the exit pile l2; changing the conveyorspeed varies the residencetime of length L.

The conveyor 5 may be disposed substantially horizontally or, asshown,may slope slightly upwardly toward the exit end of the tunnelguarded by the vibratile support 8.

Although the supporting plate 8 has been illustrated as verticallyoscillatable, this mode of vibration is shown only by way of example andcould be replaced by other modes, e.g. a swinging about a horizontalaxis.

We claim:

1. A. fluidized bed for the heat treatment of workpieces, comprising anelongated tunnel; an apertured unidirectionally movable conveyorextending within said tunnel past an exit end thereof for dischargingtreated workpieces; dispenser means at an entrance end of said tunnelfor depositing workpieces to be treated on said conveyor; circulationmeans for blowing a treatment agent through said tunnel, said treatmentagent consisting of a gas stream with entrained solid particles;vibratory support means, with an upper surface rising in the directionof conveyor motion, disposed just below said conveyor at said exit endfor arresting outwardly traveling particles and accumulating same in apile within said tunnel; and flexible seal means extending between saidsupport means and the bottom of said tunnel for blocking the escape ofparticles from said tunnel beneath said support means.

2. A fluidized bed as defined in claim 1 wherein said support means isprovided with drive means for oscillating same at a 3. A fluidized bedas defined in claim wherein said support means comprises a hollow platehaving its interior connected to said circulation means for receivingpart of said gas stream, the upper surface of said plate being aperturedfor releasing the gas from said interior into the space thereabove.

4. A fluidized bed for the heat treatment of workpieces comprising anelongated tunnel; an apertured unidirectionally movable conveyorextending within said tunnel past an exit end thereof for dischargingtreated workpieces; dispenser means at an entrance end of said tunnelfor depositing workpieces to be treated on said conveyor; circulationmeans for blowing a treatment agent through said tunnel, said treatmentagent consisting of a gas stream with entrained solid particles: andvibratory support means with an upper surface rising in the direction ofconveyor motion, disposed just below said conveyor at said exit end forarresting outwardly traveling particles and accumulating same in a pilewithin said tunnel; said support means comprising a hollow plate havingits interior connected to said circulation means for receiving part ofsaid gas stream, the upper surface of said plate being apertured forreleasing the gas from said interior into the space thereabove.

5. A fluidized bed as defined in claim 4 wherein said support means isprovided with drive means for oscillating same at a frequency ofsubstantially 20 to 40 cycles per second, said particles having a sizeranging between substantially 40 and microns.

